Canon S110 has a
12.0MP 1/1.7-inch (7.44 x 5.58 mm ) sized CMOS sensor and features Digic 5 processor. On the other hand, Canon SD4500 IS has a
10.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Digic 4 processor.
Below you can see the S110 and SD4500 IS sensor size comparison.
As seen above, Canon S110 has a 1.5x Larger sensor area than Canon SD4500 IS. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.